Flexible laminates are used in the electronics industry as the base materials for fabricating a wide variety of flexible electronic products including flexible connectors, flexible circuit boards and flex-rigid circuit boards. Flexible connectors, flexible circuit boards and flex-rigid circuit boards are used in notebook computers, printers and hard disc drives, as well as numerous medical devices and consumer products. Flexible laminates are also used for certain advanced applications such as chip-on-flex and fine-line circuit boards. With the electronics industry moving toward thinner, lighter, flexible and more functional products, the demand for flexible laminates continues to increase.
Flexible laminates are used in applications in which the number of flex cycles required varies widely. In some applications, such as a printed circuit board for use in an automobile dashboard, the laminate is flexed one time during installation. In other applications, such as in a camera, the laminate may be flexed a few hundred times during its life. In the applications to which the present invention is directed, the laminate must be capable of withstanding many thousands or even millions of flex cycles without failure. Such applications include flexible connectors for printers, computer disk drives and other high flex uses.
Electrodeposited copper foil has been used for making flexible laminates. However, the electrodeposited copper foil that has been used typically has a fatigue ductility of about 20 to 50% which may be slightly improved if the foil is heat treated. This level of fatigue ductility provides for copper foils that are acceptable for single bends. However, these copper foils have not been found to be suitable for high flex applications, requiring thousands or even millions of flexes during the life of the device with which they are used.
It would be advantageous to provide a high performance flexible laminate that could be used in making electrical connectors and flexible circuit boards that are capable of flexing thousands or millions of times over the life of the devices with which they are used. The present invention provides for such an advantage.